Transcript Spring 2015 Chapter 15

EPIDEMIOLOGY AND
NOSOCOMIAL INFECTIONS
CHAPTER 15
Copyright © 2012 John Wiley &
Sons, Inc. All rights reserved.
Epidemiology: a branch of medical science that deals with the
incidence, distribution, and control of disease in a population
Incidence and prevalence rates
Incidence- the number of new cases contracted within a set population during a specific period of
time (e.g., new cases per 100,000) .
Prevalence- total number of people infected within the population at any time.
Total infected
New cases
Fig. 15.1 incidence and prevalence rates
Morbidity and mortality frequencies
Morbidity rate= the number of individuals affected by a disease
during a set period in relation to the total number of individuals
in a population
Mortality rate is the number of deaths due to a disease in a
population during a specific period in relation to the total
population
Disease in Populations
EEE-sporadic
California Equine-endemic pattern
WEE-epidemic pattern
Fig 15.6 Incidence rate of three different types of encphalitis
Epidemiologic studiesDescriptive studies- concerned with the physical aspects of an
existing disease and disease spread and records:
1) number of cases of a disease
2) the segments of a population that were affected and
3) the locations and time period of the cases.
The age, gender, race, marital status, socioeconomic status and
occupation of each patient also are recorded.
Analysis of the data can determine whether people of a certain age
group, males or females, or members of a certain race are
particularly susceptible to the disease.
Data on marital status or sexual behavior can help show whether
the disease is transmitted sexually.
Essentially all aspects of the disease and its distribution can be
analyzed once the data is gathered.
Cholera cases centered
around the Broad Street
water pump station
In 1854, John Snow, a London physician, recorded the locations of cholera cases in the city. He found that they were
centered around the Broad Street pump, which supplied water to the nearby area. He tracked the epidemic’s source to
contamination of the pump by sewage. When the handle was removed the epidemic subsided. This has been perceived as
a major event in the history of public health and can be regarded as the founding event of the science of epidemiology.
Fig. 15.8 The first epidemiologic study
Analytical studies- focuses on cause and effect relationship in the
occurrence of diseases in populations and can be either
retrospective (examines past data to determine cause-e.g., the
relationship between smoking or second hand smoke and cancer) or
prospective- (considers factors that occur as an epidemic spreads).
For example, in 1993 hantavirus outbreak spread in the US.
Southwest, epidemiologists had to determine what was causing the
disease an how to change living conditions so that the infectious agent
would stop spreading.
Experimental studies- designs experiments to test a
hypothesis often about the value of a particular treatment.
One group gets treatment another gets placebo (the efficacy
of the polio vaccine was examined in this way). In fact
most experimental drugs are managed in this manner.
Reservoirs of infectionHuman reservoirsCarriers- individuals who harbor an infectious agent without having any observable
clinical signs or symptoms.
A chronic carrier is a reservoir of infection for a long time after he or she has
recovered from a disease.
An intermittent carrier periodically releases organisms.
Animal Reservoirs- monkeys are important reservoirs for malaria, yellow fever and
other human diseases. Diseases that can be transmitted under natural conditions to
humans from other vertebrate animals are called zoonoses.
Nonliving reservoirs- Soil and water can serve as reservoirs for pathogens. Soil- C.
tetani, C. botulinum- . Contaminated foods- SalmonellaWater- contaminated by human or animal feces can contain a variety of pathogens- V.
cholerae, polio, Legionella
Portals of Entry- ear, eye, nose, mouth, mammary glands,
urethra, vagina, anus, placenta, broken skin and seminal
vesicles
Portals of exit- essentially the same as above
When you sneeze and do not cover your nose and mouth the above occurs or how I
spread flu, tuberculosis, etc.. What is the proper way to “block” a cough or sneeze?
Fig. 15.12 Droplet transmission
a) when the percentage of immune persons in a population is low, it is likely that
susceptible individuals will be exposed to the disease (b and c). As the percentage of
immune persons increases, it becomes increasingly less likely that a susceptible
individual will be exposed to the disease. H5N1 would have very low herd immunity.
•
Carrier
status
•
STDs
•
Zoonoses
•
Disease
Cycles
•
Herd
Immunity
Fig. 15.13 Herd Immunity
Nosocomial Infections-Nosocomial infection are infections
acquired in a hospital or other medical facility.
Exogenous infections- caused by organisms that enter the
patient from the environment.
Endogenous infections are caused by opportunists among the
patient’s own normal microflora..
Opportunists are most likely to cause infection if the patient
has lowered resistance or if normal microflora have been
eliminated by antibiotics.
1
2
3
4
4
Fig. 15.20 Common causative agents of nosocomial infections
1
3
2
Fig. 15.22 Relative frequencies of sites of nosocomial infections